The use of polyvinyl alcohol as a separator material in alkaline batteries is well known. A standard electrolyte for alkaline batteries is concentrated aqueous potassium hydroxide. Although polyvinyl alcohol is soluble in water, it is not readily dissolved in such a concentrated potassium hydroxide solution, and thus, films of this material can be used in such electrolytes. In general, polyvinyl alcohol films have been utilized as battery separators because of their high conductivity in alkaline electrolytes and their ease of fabrication from aqueous solution.
Efforts have been made to improve the mechanical properties and chemical stability of polyvinyl alcohol by synthesizing numerous derivatives of the polymer. However, the number of processes for the in situ reaction of prefabricated polyvinyl alcohol structures, such as battery separators, is limited. The in situ acetalization of polyvinyl alcohol separators has been achieved through treatment of the separators with acid solutions of aldehydes, such as an aqueous formaldehyde solution containing a small amount of sulfuric acid. The aldehyde acetalates the 1,3 diol units present in the polymer thereby creating tough, water insoluble derivatives. In many of the aldehyde treatments, the extent of acetalization is difficult to control. Extensive acetalization of polyvinyl alcohol leads to poor conductivity in alkaline electrolyte, which is probably due to the decreased number of hydrophilic alcohol groups resulting from the using up of such groups by the acetalization reaction. In addition, commercially available polyvinyl alcohol normally contains approximately from 0.5% to 6%, but may be made to contain up to 20% of 1,2 diol units in the predominantly 1,3 diol polymer structures. These chemically reactive 1,2 diol units are still present in the chain and can lead to poor oxidation resistance of the polymer.
Reference is also made to U.S. Pat. No. 2,983,759 (Matsumoto et al) which mentions the preparation of polyvinyl alcohol having terminal carbonyl groups by oxidizing the polyvinyl alcohol with an agent such as periodic acid or lead tetraacetate whereby 1,2 glycol groups in the polyvinyl alcohol are cleaved and oxidized to carbonyl groups.